I have four Motorola KSN1016 drivers to use. For frequency measurements I screwed them to a sanding block and put them over the corner of a loudspeaker to get as much free space as possible.

The impedance measurements grouped  the drivers in two pairs 1&4 and 2&3. (I numbered them in random order as I saw no distinct markings on the drivers to separate one from the other,). The very high capacitive impedance shows how they can be used without any crossover (but then you can not adjust the frequency response at all). I have read that you can add a 8 ohm resistor across the driver and then it will behave like any other 8 ohm driver when using serial capacitors for cross over

Then some frequency measuremnets with Omnimic on axis about 1/2 meter distance.

The results looks quite bad. Especially for 1&4 that are all over the place and unmatched. 2&3 are at least matched and also slightly smoother. A closer look show that the level increase about 6 dB from the dip at 8 khz to the low end peak around 4 kHz. If I can get a 6 dB/octave filter starting below 8 kHz it should result in a flat respons down to 4 kHz and then a rapid drop of. I will make some test soon.
In the time domain all four drivers have some severe ringing around 4 kHz.

If I supress the output at 4 kHz by 6 dB relative to the output above 8 kHz those ridges should go down as well.